title: Akt switches TopBP1 function from checkpoint activation to transcriptional regulation through phosphoserine binding-mediated oligomerization.
abstract: Our previous study showed that Akt phosphorylates TopBP1 at the Ser-1159 residue and induces its oligomerization. Oligomerization is required for TopBP1 to bind and repress E2F1 activity. However, the mechanism through which phosphorylation of TopBP1 by Akt leads to its oligomerization remains to be determined. Here, we demonstrate that binding between the phosphorylated Ser-1159 (pS1159) residue and the 7th and 8th BRCT domains of TopBP1 mediates TopBP1 oligomerization. Mutations within the 7th and 8th BRCT domains of TopBP1 that block binding to a pS1159-containing peptide block TopBP1 oligomerization and its ability to bind and repress E2F1 activities. The Akt-induced TopBP1 oligomerization is also directly demonstrated in vitro by size exclusion chromatography. Importantly, oligomerization perturbs the checkpoint-activating function of TopBP1 by preventing its recruitment to chromatin and ATR binding upon replicative stress. Hyperactivation of Akt inhibits Chk1 phosphorylation after hydroxyurea treatment, and this effect is dependent on TopBP1 phosphorylation at Ser-1159. Thus, Akt can switch the TopBP1 function from checkpoint activation to transcriptional regulation by regulating its quaternary structure. This pathway of regulation is clinically significant, since treatment of a specific Akt inhibitor in PTEN-mutated cancer cells inhibits TopBP1 oligomerization and causes its function to revert from promoting survival to checkpoint activation.
authors.affiliation: Section of Hematology/Oncology, Departments of Medicine and Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Kang
authors.initials: K
authors.lastname: Liu
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Graves
authors.forename: Jessica D
authors.initials: JD
authors.lastname: Scott
authors.forename: Rongbao
authors.initials: R
authors.lastname: Li
authors.forename: Weei-Chin
authors.initials: WC
authors.lastname: Lin
mesh_terms: D019943:Amino Acid Substitution; D002352:Carrier Proteins / Q000737:chemistry / Q000502:physiology*; D059447:Cell Cycle Checkpoints; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D050687:E2F1 Transcription Factor / Q000378:metabolism; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006575:Heterocyclic Compounds, 3-Ring / Q000494:pharmacology; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D056004:Molecular Dynamics Simulation; D009687:Nuclear Proteins / Q000737:chemistry / Q000502:physiology*; D010766:Phosphorylation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D011499:Protein Processing, Post-Translational; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D013312:Stress, Physiological; D014158:Transcription, Genetic
chemical_list: D002352:Carrier Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D006575:Heterocyclic Compounds, 3-Ring; C548887:MK 2206; D009687:Nuclear Proteins; C110513:TOPBP1 protein, human; D012694:Serine; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt; D006918:Hydroxyurea